1. Field
The invention relates generally to the control of a fluid displacement apparatus, by controlling the volume of fluid displaced or transmitted through such apparatus in response to an external parameter. More specifically, this invention relates to a rotary vane compressor frequently utilized for passenger compartment air conditioning on automobiles. In such compressors, retention of the vanes in their retracted position stops the pumping action. The present invention discloses a control circuit to provide for vane retention in the retracted position to modulate the compressor output in response to changing engine speeds, and cooling loads. It retains the present clutch mechanism for complete disengagement of the compressor from the driving means.
2. Prior Art
Control of the output or discharge from a compressor or rotary vane fluid displacement apparatus by control of the vanes has been demonstrated in the art. Methods usually employed to retain or retract these vanes utilize a mechanical clamping device, electromechanical device, control of a clutch or the use of a regulator valve to control the discharge pressure. U.S. Pat. No. 2,280,272 to Sullivan discloses a blade guide to maintain the blades or vanes in contact with the compression chamber wall. The outlet pressure in Sullivan U.S. Pat. No. 2,280,272 is regulated with a regulating valve at the regulating port. A fluid motor as taught in U.S. Pat. No. 3,153,984 (Fiske) utilizes a flexible spring subject to fluid pressure to maintain the vanes extended from the guide slits in a compression chamber of such fluid displacement apparatus. The vanes in this fluid motor are displaced into the guide slits as they pass fulcrum points on the pressure chamber wall but are not retained in the guide slits. A rotary vane pump generally for use with an hydraulic transmission is disclosed in U.S. Pat. No. 3,455,109 (Daniels) wherein vane movement within or displacement from the guide slit is controlled through a pilot valve, clutch means and double-acting piston arrangement operable at the root of the vane guide slits. Fluid is introduced to either side of the double-acting piston to extend or retract the vanes. U.S. Pat. No. 3,828,569 (Weisgerber) teaches the use of refrigerant fluid to force the vanes to radially extend themselves to maintain contact with the pressure chamber wall. U.S. Pat. Nos. 4,050,263 and 4,103,506 (Adalbert et al.) recognize the value of modulating the flow of an automobile air conditioning compressor by maintaining the vanes of a rotary vane compressor in the retracted mode. The vanes, in this instance, are retained by a locking member actuated by a solenoid which is responsive to engine speed. The locking member is moved axially to contact a projection of a vane, and in fact, the vanes are arrested in pairs, as taught therein. U.S. Pat. No. 4,061,450 (Christy) discloses a set of mechanically connected arms and vanes where such arms are joined to a journal to provide reciprocal movement to the vanes during rotation of the rotor.